Recently, Associate Professor Zhimiao Yan and Professor Benlong Wang from the Department of Engineering Mechanics develop an origami mechanical metamaterial that can reprogram deformation modes and mechanical properties through functional group and ring reconfiguration. This mechanical metamaterial could provide a versatile material platform and a universal structural design paradigm for reprogrammable mechanical computing, multi-purpose robots, transformable vehicles and architectures at different scales. This work is recently published in the journal Nature Communications (A reprogrammable mechanical metamaterial with origami functional- group transformation and ring configuration, vol. 14:6709). The first author is Xinyu Hu, a Ph. D. candidate in the Department of Engineering Mechanics.

Mechanical metamaterials represent a category of innovative materials that, by designing specific physical elements, surpass the constraints of certain natural laws and achieve unique mechanical properties, such as alternating Poisson's ratio, multi-stability, negative compressibility, chirality and tunable stiffness. Structural reconfigurability endows mechanical metamaterials with reprogrammable and controllable properties, which enhances the breadth and depth of the application prospects of the designed materials themselves.

Currently, mechanical metamaterials are composed of periodic mono-characteristic homo-elements, such as complete-elastic (C) elements with positive stiffness or rigid-elastic (R) elements with negative stiffness, which cannot be converted to each other. Mono-mechanical and mono-deformation characteristic limits their reprogramming functions. To achieve rich reprogrammable mechanical properties, this work couples C and R elements to form C or R functional groups, and then uses the same functional group to create C or R-ring metamaterials. The complete-elastic and rigid-elastic elements are created through the origami mechanism. The C and R elements can be transferred between adjacent functional groups in the ring metamaterial, allowing for reversible mutual transformation between C and R-ring metamaterials. The ring metamaterial composed of heterogeneous elements can serve as the unit cell for constructing periodic homogeneous metamaterials. Two types of metamaterials, triangular and quadrilateral one, are designed. quadrilateral ring metamaterial provides more reconfigurability and greater reprogrammability than triangular one due to its unique structure.

The same functional groups are connected end-to-end to construct ring metamaterials. This metamaterial exhibits multimodal deformation characteristics due to different applied force modes. When it undergoes torsional deformation under internal and external torques, it can achieve torsional contraction, torsional expansion, or both of torsional contraction and expansion based on deformable elements. For quadrilateral ring mechanical metamaterials, in addition to torsional deformation, they can also achieve uniaxial deformation with a Poisson's ratio of 0 and auxetic deformation with a Poisson's ratio of -1, which discretely regulates the mechanical properties of metamaterials. The rings in periodic metamaterials can independently switch between C and R functional modes without interfering with each other. These advantages make this metamaterial suitable for various applications, including load-bearing, soft driving, and mechanical computing.

The designed metamaterial can be utilized to build the body components such as legs and arms. The unique characteristics of reprogrammable stiffness modulus, achieved through functional group transformation and ring configuration, ensure that the material exhibits low stiffness during motion to provide vibration isolation and high stiffness to support heavy loads. the proposed metamaterials can act as actuators for robots through internal electric drive. The axial and torsional deformations enable the actuator to adapt to different environmental conditions and perform various tasks. It can be used to anchor machines and facilitate cargo delivery in narrow environments like pipelines, through torsional and axial deformations with negative Poisson’s ratio. Acting as a connecting role within a large-scale integrated circuit, this field-reprogrammable gate array also determines whether the logic circuit module runs after the output d, thereby enriching information processing capabilities through functional group transformation.

Paper link: https://www.nature.com/articles/s41467-023-42323-1